According to
its website,
the Sociedad Bascongada de los Amigos del País grew from
meetings and assemblies held in the home of the
Conde de Peñaflorida.
In 1763 plans were drawn up to formalize this Society,
in 1764 it was actually founded in Vergara, and
in 1765 it was approved at a general assembly.

It is difficult to determine the date when the Royal designation was
added.
Its earliest publications suggest that it did not have the Royal
designation in 1766 and 1772.
A record in the
Bib. Nac. España cat.
lists the following 1780 publication:
Catalogo general alfabético de los individuos de la Real
Sociedad Bascongada de los Amigos del País, a fines de diciembre...
de 1780,
which establishes that the Royal designation was in use as early as 1780.

Boletín de la Real Sociedad Vascongada de Amigos del
País
The record in the
Bib. Nac. España cat.
gives the numbering as 1945, 1er. trim. - (Año 1 - ), and indicates
that part of the time the title was
Boletín de la Real Sociedad Bascongada de los Amigos
del País.
The records in the
Zeitschriftendatenbank (ZDB) are more precise;
they indicate that for 1.1945 - 13.1957 the title was
Boletín de la Real Sociedad Vascongada de Amigos del
País, but that the title from then until 31.1975 was
Boletín de la Real Sociedad Vascongada de Amigos del
País.
This title had several supplements, including D.
Continued by D.
[Bib. Nac. España cat.;
Zeitschriftendatenbank (ZDB)]